Consumer products can provide a hospitable environment for rapid microbial growth. Such exposure can, and frequently does, result from inadvertent microbial inoculation of the product during manufacturing or packaging. Spoilage microorganisms, for example in food products, can then rapidly proliferate by feeding on nutrients provided by the product.
Preservatives, such as sorbates, benzoates, organic acids, and combinations thereof have been used in various products, particularly foods and beverages, to provide some degree of microbial inhibition. However at levels effective to inhibit microbial growth, some of these preservatives can contribute off-flavors in the product, thus making the product undesirable for its intended purpose. Similarly, natural preservatives, such as natamycin, are frequently used in food and beverage products to inhibit microbial growth. Unfortunately, while these natural preservatives may be effective against either yeast or bacteria, they may not be effective against both.
It has been disclosed that the essential oil of mustard plants, which contain isothiocyanates, exhibits an antibacterial and antimycotic effect in oral therapies and on certain foods. See e.g., Sekiyama et al., U.S. Pat. No. 5,334,373, assigned to Nippon Sanso Corp., issued Aug. 2, 1994; and Madaus et al., U.S. Pat. No. 3,998,964, issued Dec. 21, 1976. The isothiocyanate compounds in mustard essential oils are the active agents that provide the antimicrobial effect. The essential oil derived from white or yellow mustard plants (Sinapis alba or Brassica alba), also provides the foregoing antibacterial and antimycotic benefits. Additionally, isothiocyanate compounds are effective antimicrobial agents at relatively low usage levels. The principal isothiocyanate present in the white mustard essential oil, 4-hydroxybenzyl isothiocyanate (4-HBITC), is a moisture sensitive compound that begins to degrade (i.e. hydrolyze) within hours of being exposed to moisture. When degraded, the 4-hydroxybenzyl isothiocyanate forms, among other compounds, 4-hydroxybenzyl alcohol.
However, the isolation and extraction of white mustard essential oils from mustard plants presents problems. Unlike most of the other plant essential oils that are volatile and can be steam distilled, white mustard essential oil is not volatile at atmospheric pressure and requires that it be extracted out of the seeds by the use of a solvent or a method such as supercritical fluid extraction. Additionally white mustard essential oil, unlike most of the other plant essential oils, is relatively unstable, especially so when exposed to moisture. This instability imposes the additional condition that when the essential oil is generated that it be extracted from the mustard seed and soon stabilized thereafter to maintain its antimicrobial properties.
Currently, the mustard processing industry makes use of the white mustard flour primarily while the essential oil is largely ignored. In fact, to make use of the white mustard flour without the “heating” sensation of mustard, the ground mustard flour is subjected to a thermal deactivation step. Here, the enzyme myrosinase, which catalyzes the formation of 4-hydroxybenzyl isothiocyanate from its precursor 4-hydroxybenzylglucosinolate, also known as sinalbin, is intentionally deactivated so that the essential oil does not form when the flour is mixed with moist food products such as meat and sausage. Additionally, because of its instability, 4-hydroxybenzyl isothiocyanate is not currently available commercially, whether as a natural product or as a pure chemical.
Accordingly, white mustard essential oil has not been widely known or widely utilized in the art for its antibacterial and antimycotic effect. However, the present inventors have surprisingly discovered that, in one embodiment, by generating the white mustard essential oil by adding water to defatted ground mustard seed, extracting the white mustard essential oil using solvents or supercritical fluids, drying the essential oil by removing the solvent and residual moisture, and then intimately blending the resulting white mustard essential oil with a hygroscopic carrier, the moisture sensitive isothiocyanate compounds contained therein can be stabilized. Hence, the blend of white mustard essential oil with a hygroscopic carrier is, thereafter, capable of being used as an effective antibacterial and antimycotic agent for solid food products. The scaling up issues involved in making white mustard essential oil on a larger scale and instability of white mustard essential oil has not been recognized by others involved in extracting essential oils. For example, some of the publications involved describe a first solvent extraction step to remove the fixed or triglyceride component of mustard oil followed by de-solventizing the defatted mustard seed prior to activation with water to generate the active component 4-hydroxybenzyl isothiocyanate.
Other earlier attempts to make WMEO comprised of the following steps as described in the referenced art. First solvent extracting the ground mustard seed to remove all of the fixed oils, drying the seed, wetting with water and allowing the 4-HBITC generating reaction to proceed for up to 24 hours, extracting the moistened mustard seed residue with acetone, removing the acetone under reduced pressure and extracting the residue with 96% ethanol to yield a solution of the active component 4-HBITC as described in DE2046756A. GB 224524 describes solvent extracting or pressing out the fixed oil from mustard seed and then adding water to create a pasty mass that is allowed to react for 24 to 48 hours in order that the sinalbin precursor is converted to sinalbin mustard oil. After pressing this pasty mass to remove water, myrosinase, sinapic bisulfate, sugar, and traces of 4-HBITC, the residue as well as the pressed extract is solvent extracted with diethyl ether and the ether removed under reduced pressure to yield sinalbin oil. U.S. Pat. No. 6,824,796 describes a process for extracting the isothiocyanates from leafy vegetables and roots such as horseradish. Here vegetable oil is used as the solvent for the isothiocyanates after activation of the myrosinase catalyst by grinding the plant material in water. The scientific literature also describes methods based on first de-fatting mustard seed using solvents, then drying the seed to rid it of any residual solvents, crushing the de-fatted seed in water and allowing the reaction to proceed for about 24 hours in the presence of a solvent (Borek, V. & Morra, M. J. 2005. Ionic thiocyanate production from 4-hydroxybenzyl glucosinolate contained in Sinapis alba meal. Journal of Agricultural and Food Chemistry, 53, 8650-8654. Vaughn, S. V. and Berhow, M. A. 2005. Glucosinolate hydrolysis products from various plant sources: pH effects, isolation and purification. Industrial Crops and Products, 21, 193-202.). In all of these instances the full potential of the myrosinase system has not been utilized and moreover as a result the time & other logistics of the extraction process do not provide viable conditions to make the essential oil of white mustard seed in any industrial sized quantity in an economical manner.
Some of the procedures above add a very high cost to the overall process and the additional burden of dealing with another solvent removal and evaporation step. Some others do not attempt to accelerate the reaction by the addition of known activators of the myrosinase enzyme such as ascorbic acid thus making a large scale process very inefficient and time consuming. Process efficiencies that can be realized by using the proper ratio of partially defatted mustard seed, water, and ethyl acetate that allows a low speed centrifugation step to separate the solvent containing the white mustard essential oil have also not been revealed in the literature.